Optically-active ortho-substituted mandelic acid compounds are compounds useful in production of medicines, agricultural chemicals and so on, and production processes using asymmetric reducing reagents or the like have been proposed, but in the process described in International Publication No. WO 0210101, further recrystallization or the like is performed after a reaction in order to increase an optical purity and, also in a reaction described in Organic Letters, 2005, vol. 7, No. 24, 5425-5427, it cannot be necessarily said that an optical yield of the reaction is sufficient, In addition, has not been known a method of asymmetrically reducing a keto group of a phenylglyoxylic acid compound, the group having a substituent at an ortho-position and being in the sterically-complicated environment, to an optically-active mandelic acid compound using a microorganism or the like.